First off, the 8 player version. I can safely say this is a hot mess of a game, barely a shadow of the expected 7 wonders experience. If someone asks you to play 8 player 7 Wonders as a "team game" you will have more fun standing in the corner that trying to eek out an empire with the guy one seat to the right looking over your shoulder.
The beauty of the 7 player game is in how fast things happen. All turns happen simultaneously, all you have to do is decide which card to take. Now imagine each decision on card choice being decided by a committee of two. Instead of picking your card in a typical "gut decision," you end up picking the card neither of you have any particularly strong objections to. Perhaps this would be fun if you were a Bynar. It was not fun for humans.
It was with trepidation (and not trepanation) that I attempted the 2 player variant. With 2 players, each human player trades on one side with their opponent, and on the other with a robot 3rd player. Yep, that's right, robot 3rd player. Doesn't sound very promising.
I was surprised, surprised indeed by how well it worked.
Each player takes turns controlling the 3rd player. The turn order is established by a "free city" card which is passed back in forth with one of the hands. If you look at your current hand and it has the weird card in it, you know to also pick a card for the 3rd player.
You can do all sorts of things using this extra civilization. You can make him trade with you instead of your opponent. In fact, my wife used the 3rd player to constantly trade with her civilization to amass a considerable fortune.
you can also use the 3rd player to bury a card you don't want your real opponent to have. Just make sure you don't end up giving away too many good cards to him, so that you begin to envy his board position as the game progresses.
That said, the biggest asset 7 Wonders has going...the speed and simplicity of play..is maintained by the 2 player variant. Meaning I have a number of duels to look forward to. Delighted!